The present invention relates to a process for controlling a brake system with anti-locking and/or traction slip control. In the event of control, brake pressure is sequentially modulated in the individual control channels. For this purpose, a master cylinder is connected to the wheel brakes individually and/or in groups through multi-way valves open in the basic position and re-switchable to the blocking position and a modulator is coupled to the master cylinder. The modulator, through auxiliary pressure equally controlled by multi-way valves, provides a force component counter-acting the pedal force. Through wheel sensors, the rotating pattern of the wheels is determined and electrical signals for controlling the multi-way valves are generated. A circuit configuration for carrying out the process is also provided by the present invention.
Processes and brake systems of this type have been described, wherein, for anti-locking control purposes, the brake pressure in the wheel brakes of the individual wheels or in wheel groups is sequentially modulated in a so-called time multiplex operation. U.S. Pat. Nos. 4,659,153 and 4,702,531 describe hydraulic brake systems comprising a single or tandem master cylinder coupled to a vacuum pressure booster or a hydraulic booster for pedal force boosting. Provided in each pressure fluid conduit leading from the master cylinder to the controlled wheels is a 2-way/2-position valve which is open in the resting position. Through temporary exchange of the vacuum pressure connection with the atmospheric connection of the vacuum servo aggregate or, in the event of a hydraulic booster, through bypassing the auxiliary pressure to the opposite front face of the booster piston, an auxiliary force counter-acting the pedal force is generated for anti-locking control purposes. The pressure within the working chambers of the master cylinder is decreased through the auxiliary force, thereby causing pressure fluid to flow back through the 2-way/2-position valve switched to the passage position from the associated wheel brake, whereas in the remaining wheel brakes, the brake pressure is kept constant through reswitching the respective 2-way/2-position valves to the blocking position. Thereafter, the pressure fluid conduit to another wheel brake is released while the other wheel valves are blocked, thereby adjusting successively, (i.e., sequentially) the brake pressure in all wheel brakes to the desired value. The principle of sequential modulation does not preclude brake pressure in several wheel brakes being modulated in parallel once a cophasal pressure change is caused in the wheel brakes. In rapid changes in pressure and auxiliary force, identical results can be attained, at least theoretically, by sequential modulation and by a control in parallel of the brake pressure in all control channels.
The speed at which brake pressure can be decreased and re-increased during an anti-locking control, is of utmost importance for control quality and driving stability, respectively, for attaining short stopping distances and for comfort during the control. It is, therefore, a disadvantage that between successive control operations (i.e., between blocking of the pressure fluid conduit leading to the brake in which the pressure has just been changed and connection of the next wheel brake to the master cylinder) waiting times must always be tolerated. For example, once the pressure in a control channel is to be decreased, the pressure in the master cylinder will first have to be decreased to a value below the pressure prevailing in the wheel brake. If a pressure increase is required after completion of a pressure change operation, essentially the same problem arises. The required waiting times are relatively extended because the actual pressure level in the working chambers of the master cylinder, in the modulator coupled ahead thereof, and in the wheel brakes, is not known as pressure sensors are not provided for cost saving reasons. Consequently, the pressure in the master cylinder and in the modulator coupled ahead thereof, prior to opening the conduit leading to the wheel brake will always have to be decreased and increased, respectively, to an extent such that the pressure in the master cylinder "reliably" is below and above. respectively, the pressure in the wheel brake.